1. Field of the Invention
The present invention generally relates to a rolling contact bearing assembly and, in particular, to an angular contact bearing assembly.
2. Description of the Prior Art
In a rolling contact bearing assembly in a machine tool for the support of a high speed rotating main shaft of the machine tool, with an increase in speed of rotation of the main shaft, an air oil lubricating system, an oil mist lubricating system, a jet lubricating system or the like is generally employed. Since any one of those lubricating systems employs a pumping device for jetting the lubricant, requiring a complicated fluid circuit, a grease lubricating system is still largely practiced due to its excellent maintenance.
In the grease lubricating system, grease is filled inside the bearing assembly, more specifically, in gaps delimited among various component parts such as, for example, rolling elements, inner and outer races and ball or roller retainers. In this case, where the quantity of grease retained in the various gaps is small, a problem occurs in that the length of time over which the lubrication can be effected tends to be shortened.
Although the quantity of the grease filled in the gaps in the bearing assembly can be increased to some extent, the filling of the grease in an increased quantity may bring about such problems that the resistance induced by a stirring of the grease evolves a relatively large amount of heat and that a make-ready operation to facilitate a discharge of the excessive grease and/or to stabilize the operativity of the bearing assembly takes a relatively long time. Especially in the case where the bearing assembly is used in the machine tool, the heat evolved in the bearing assembly adversely affects a machining tolerance and must therefore be minimized.
In an attempt to increase the liftime during which the lubricating system works satisfactorily, the Japanese Laid-open Utility Model Publication 64-718 has suggested the provision of a grease reservoir in a ball or roller retainer so that the grease or a base oil thereof can be supplied through one or more minute through-holes relying on the fluidity thereof. However, there is no sufficient space available in the retainer for the formation of the grease reservoir and, furthermore, a sufficient effect of suppressing the flow of the lubricant cannot be obtained because of a processing limitation in defining a bore size of the through-holes and, therefore, the lubricant tends to be supplied excessively.